To model such diffuse (spatially spread) noise,
a multichannel extension of nonnegative matrix factorization
(multichannel NMF: MNMF) [1]}, [2]}, [3]}
was proposed.
MNMF estimates a full-rank spatial covariance matrix (SCM) [4]},
which represents the time-invariant spatial characteristics of each source.
However, since the number of parameters in MNMF is large, its optimization requires a huge computational cost and
lacks robustness against the initialization [5]}.
